Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive, an electrolyte and a lithium ion battery. The electrolyte additive comprises a compound I, the structure of the compound I contains an ethylene sulfate group and a phosphoryl fluoride group, and a variable functional group R of the compound I is selected from any one of halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy and a sulfate group; the substituent group is selected from at least one of halogen and alkyl. An ethylene sulfate group can form a sulfur-containing SEI film on the negative electrode side, so that the diffusion efficiency of lithium ions is improved, and side reactions are reduced; the phosphoryl fluoride derivative can generate a CEI film rich in P and N on a positive electrode, so that the structural collapse of the ternary material under a high SOC working condition is inhibited, and the synergistic effect of the phosphoryl fluoride derivative and the ternary material can reduce the interface impedance of CEI / SEI, avoid the loss of active lithium and improve the high-temperature cycle performance of the battery; in addition, the phosphoryl fluoride group can be combined with HF in the electrolyte, PF5 is stabilized, and the high-temperature safety performance of the battery is improved.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles and energy storage systems, high-energy-density lithium-ion batteries, especially ternary batteries using nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) cathode materials, have become the mainstream choice in the market. However, the performance stability of ternary batteries in high-temperature environments faces severe challenges. The deficiencies in high-temperature performance of ternary batteries not only limit their reliability and lifespan in hot climates or high-power applications, but also constitute a key bottleneck for their large-scale commercial application. Therefore, improving the structural stability and interface compatibility of ternary batteries at high temperatures has become a core technological requirement for overcoming their application limitations and promoting the development of next-generation high-performance lithium-ion batteries. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte additive, an electrolyte, and a lithium-ion battery, which aims to solve the problem of capacity decay in existing lithium-ion batteries under high temperature and high voltage operating conditions.

[0004] The first embodiment of this application provides an electrolyte additive, comprising compound I, the structural formula of which is shown in Formula I:

[0005] Formula I; Wherein, R is selected from any one of halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted alkoxy; the substituent is selected from at least one of halogen, hydrocarbon and sulfate ester groups.

[0006] In some embodiments, R is selected from any one of halogen, substituted or unsubstituted C2-C4 alkyl, C3-C5 alkenyl, C4-C6 alkynyl and substituted or unsubstituted C2-C4 alkoxy; the substituent is selected from at least one of halogen, C1-C3 hydrocarbon and vinyl sulfate group.

[0007] In some embodiments, compound I is selected from any one of the compounds shown in Formulas I-1 to I-6:

[0008] The second embodiment of this application provides an electrolyte including the electrolyte additives described in any of the above embodiments, wherein the mass percentage of the electrolyte additives in the electrolyte is 0.5-1%.

[0009] In some embodiments, the electrolyte further includes sulfonyl lactones, wherein the mass ratio of the sulfonyl lactones to compound I is (0.5–1.5):(0.5–1).

[0010] In some embodiments, the sulfonyl compounds include at least one of 1,3-propenesulfonyl lactone and 1,3-propanesulfonyl lactone.

[0011] In some embodiments, the electrolyte further includes a lithium-containing compound, wherein the mass ratio of the lithium-containing compound to compound I is (0.5-1):(0.5-1).

[0012] In some embodiments, the lithium-containing compound includes at least one of lithium tetrafluoroborate and lithium difluorooxalate borate.

[0013] In some embodiments, the electrolyte further includes an organic solvent and a lithium salt; The organic solvent includes cyclic carbonates and chain carbonates; The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium bis(trifluoromethylsulfonyl)imide, and the lithium salt has a mass percentage of 12-15% in the electrolyte.

[0014] The third embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte in any of the above embodiments; the high-temperature storage capacity retention rate (28 days, 60°C) of the lithium-ion battery is 88.9~92.4%, and the high-temperature cycle capacity retention rate (45°C, 350 cycles) is 86.2~89.8%.

[0015] This application provides an electrolyte additive, comprising compound I, wherein the structure of compound I contains an ethylene sulfate group and a phosphoryl fluoride group, and its variable functional group R is selected from any one of halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy and sulfate groups; the substituent is selected from at least one of halogen and hydrocarbon groups. The electrolyte additive provided in this application contains both vinyl sulfate groups and phosphoryl fluoride groups. In terms of interfacial film construction, the vinyl sulfate groups preferentially undergo redox decomposition on the positive and negative electrode surfaces, generating products containing Li₂SO₃ and Li₂SO₄. The released SO₂ further promotes uniform film distribution. Meanwhile, the LiF and Li₃PO₄ produced by the decomposition of the phosphoryl fluoride groups enhance the mechanical strength and ionic conductivity of the film. These two components form a chemically bonded organic-inorganic composite framework, significantly improving the flexibility and stability of the positive and negative electrode interfacial film and reducing interfacial impedance. Regarding free radical suppression, the SO₂ from the decomposition of the vinyl sulfate groups effectively captures alkyl free radicals generated by electrolyte degradation, while the phosphoryl fluoride groups suppress combustion by capturing oxygen-containing free radicals and exerting gas-phase dilution and condensed-phase carbonization effects. This dual mechanism efficiently terminates free radical chain reactions, reducing the risk of electrolyte gas generation and thermal runaway. In terms of transition metal dissolution control, SO₂ reduces Ni dissolution through complexation. 3+ Co 3+ The free concentration of plasma is reduced, and the phosphoryl fluoride group anchors the dissolved ions to the positive electrode surface through chemical coordination, forming a dual kinetic-thermodynamic barrier, which greatly reduces the damage of metal ion migration to the electrolyte and interface film. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 These are battery test results provided in the embodiments and comparative examples of this application. Detailed Implementation

[0018] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0019] In the description of this application, it should be noted that "multiple" means two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features.

[0020] The compounds of this application can be synthesized via synthetic routes including methods similar to those known in the field of chemistry, particularly with reference to the description contained herein. Starting materials are generally available from commercial sources or can be readily prepared using methods known to those skilled in the art. For illustrative purposes, the reaction schemes described below illustrate possible routes for synthesizing the compounds of this application and key intermediates. For a more detailed description of each reaction step, see the Examples section below. Those skilled in the art will recognize that other suitable starting materials, reagents, and synthetic routes can be used to synthesize the compounds of this application and their various derivatives.

[0021] Unless otherwise stated, the term "alkyl" as used herein refers to a saturated aliphatic hydrocarbon group, which may be straight-chain or branched. For example, the term "C1-C6 alkyl" refers to an alkyl group containing 1, 2, 3, 4, 5, or 6 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, neopentyl, hexyl, 2-methylpentyl, etc.). Similarly, the alkyl portion (i.e., alkyl) of alkoxy, alkylacyl, alkylphosphate, alkylsulfonyl, and alkylaminosulfonyl groups has the same definition above. For example, the term "C1-C3 alkyl" refers to an alkyl group containing 1, 2, or 3 carbon atoms (e.g., methyl, ethyl, propyl, and isopropyl). Alkyl groups may be substituted or unsubstituted, and when substituted, the substituents may be substituted at any usable link.

[0022] Unless otherwise stated, the term "hydrocarbon group" as used herein refers to a monovalent chain group consisting of carbon and hydrogen atoms. Hydrocarbon groups can be straight-chain or branched, saturated or unsaturated, and substituted or unsubstituted. Non-limiting examples of hydrocarbon groups include, but are not limited to, alkyl, alkenyl, or ynyl groups. For example, the term "C2-C5 hydrocarbon group" refers to a monovalent straight-chain or branched alkyl, alkenyl, or ynyl group having 2 to 5 carbon atoms. Non-limiting examples of C2-C5 hydrocarbon groups may include, but are not limited to, n-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, lauryl, butenyl, hexenyl, octenyl, decenyl, myrceneyl, octynyl, etc.

[0023] 3-Butenyl, 2-pentenyl, hexenyl, octenyl, decenyl, myrceneyl, etc.

[0024] Unless otherwise stated, the term "halogen" as used herein refers to fluorine, chlorine, bromine, or iodine.

[0025] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure of this application, the configuration and arrangement of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0026] For ternary cathode materials in batteries, high temperatures accelerate the structural degradation of the cathode material and the dissolution of transition metal ions, leading to significant capacity decay and shortened cycle life. At the same time, it exacerbates electrolyte decomposition and interfacial side reactions, increasing the battery's internal resistance. More seriously, high temperatures significantly increase the risk of thermal runaway in batteries, which can lead to fires, explosions, and other safety accidents.

[0027] The applicant discovered through research that by adding additives containing both vinyl sulfate groups and phosphoryl fluoride groups to the electrolyte, the chemical properties of the electrolyte and the physicochemical characteristics of the electrode surface can be improved, effectively solving the problem of battery capacity decay at high temperatures from multiple aspects, thereby extending the battery's calendar life.

[0028] The first embodiment of this application provides an electrolyte additive, including compound I, the structural formula of which is shown in Formula I:

[0029] Formula I; Wherein, R is selected from any one of halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted alkoxy; the substituent is selected from at least one of halogen, hydrocarbon and sulfate ester groups.

[0030] It is understood that the structure of compound I contains a vinyl sulfate group and a phosphoryl fluoride group, and its variable functional group R is selected from any one of halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy and sulfate groups; the substituent is selected from at least one of halogen and hydrocarbon groups. The electrolyte additive provided in this application contains both vinyl sulfate groups and phosphoryl fluoride groups. In terms of interfacial film construction, the vinyl sulfate groups preferentially undergo redox decomposition on the positive and negative electrode surfaces, generating products containing Li₂SO₃ and Li₂SO₄. The released SO₂ further promotes uniform film distribution. Meanwhile, the LiF and Li₃PO₄ produced by the decomposition of the phosphoryl fluoride groups enhance the mechanical strength and ionic conductivity of the film. These two components form a chemically bonded organic-inorganic composite framework, significantly improving the flexibility and stability of the positive and negative electrode interfacial film and reducing interfacial impedance. Regarding free radical suppression, the SO₂ from the decomposition of the vinyl sulfate groups effectively captures alkyl free radicals generated by electrolyte degradation, while the phosphoryl fluoride groups suppress combustion by capturing oxygen-containing free radicals and exerting gas-phase dilution and condensed-phase carbonization effects. This dual mechanism efficiently terminates free radical chain reactions, reducing the risk of electrolyte gas generation and thermal runaway. In terms of transition metal dissolution control, SO₂ reduces Ni dissolution through complexation. 3+ Co 3+ The free concentration of plasma is reduced, and the phosphoryl fluoride group anchors the dissolved ions to the positive electrode surface through chemical coordination, forming a dual kinetic-thermodynamic barrier, which greatly reduces the damage of metal ion migration to the electrolyte and interface film.

[0031] In some embodiments, R is selected from any one of halogen, substituted or unsubstituted C2-C4 alkyl, C3-C5 alkenyl, C4-C6 alkynyl and substituted or unsubstituted C2-C4 alkoxy; the substituent is selected from at least one of halogen, C1-C3 hydrocarbon and vinyl sulfate group.

[0032] In some embodiments, compound I is selected from any one of the compounds shown as compound I-1 to compound I-6:

[0033] The above compounds can be prepared using methods known in the art, for example: 1) Cyclization: Under argon protection, glycerol was dissolved in anhydrous dichloromethane. With vigorous stirring, anhydrous pyridine and freshly distilled thionyl chloride were simultaneously and slowly added dropwise over 1.5 hours through two constant-pressure dropping funnels, with strict temperature control. After the addition was complete, stirring was continued at -78°C for 1 hour, followed by a slow rise to 0°C. The resulting pyridine hydrochloride precipitate was quickly removed by filtration. The filtrate was then rotary evaporated under reduced pressure at 0°C to obtain a pale yellow oily intermediate (1-hydroxymethyl-vinyl sulfite), which could be used directly in the next step without further purification.

[0034] 2) Phosphorylation: The above-mentioned 1-hydroxymethyl-vinyl sulfite was dissolved in anhydrous acetonitrile. Under argon protection at 0°C, phosphoryl fluoride (POF3) gas (excess) was slowly introduced, and the reaction was stirred for 2 hours. After the reaction was completed, nitrogen gas was introduced to remove excess POF3, and the mixture was concentrated under reduced pressure to obtain a colorless oily intermediate 1-((fluorophosphoryl)oxy)methyl-vinyl sulfite.

[0035] 3) Oxidation: The above phosphorylated intermediate was dissolved in ethyl acetate, and excess m-chloroperoxybenzoic acid was added. The mixture was stirred at room temperature for 4 hours. After the reaction was completed, saturated sodium thiosulfate solution was added to quench the excess oxidant. After separation, the organic phase was washed three times with saturated sodium bicarbonate solution, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain the colorless oily product of formula I.

[0036] The second embodiment of this application provides an electrolyte including the electrolyte additives in any of the above embodiments, wherein the mass percentage of the electrolyte additives in the electrolyte is 0.5~1%.

[0037] It is understandable that the mass percentage of electrolyte additives in the electrolyte can be any value from 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value within a range of any two values. By controlling the amount of compound I added to the electrolyte to meet the above range, it is possible to ensure the formation of stable and dense SEI / CEI films at both the positive and negative electrodes of the battery, while reducing the interfacial impedance of CEI / SEI, avoiding the loss of active lithium, and improving the high-temperature cycle performance of the battery.

[0038] In some embodiments, the electrolyte further includes sulfonyl lactones, wherein the mass ratio of sulfonyl lactones to compound I is (0.5–1.5):(0.5–1).

[0039] It is understandable that the mass ratio of sulfonyl lactone to compound I can be any value among 1:1, 1:2, 2:1, 3:1, 3:2 or any value within a range of any two values. The core of sulfonyl lactone compounds relies on the strong electron-withdrawing properties of their sulfonyl lactone ring (-SO2-O-) functional group to optimize battery performance through multiple mechanisms: their energy level characteristics, which are adapted to the positive and negative electrode interface reactions, allow them to preferentially decompose at the negative electrode before the main solvent to generate a dense SEI film containing lithium sulfonates and sulfates, blocking the continuous reaction between the electrolyte and the negative electrode and inhibiting lithium dendrite growth. At the same time, under high voltage, they preferentially oxidize at the positive electrode to form a uniform CEI film, thereby reducing the oxidation activity of the positive electrode and reducing the dissolution of transition metal ions. Their decomposition products can capture active free radicals generated during electrolyte cycling, terminating the electrolyte decomposition chain reaction, and oxygen atoms can form stable coordination complexes with dissolved transition metal ions, weakening their catalytic degradation effect on the electrolyte. In addition, their polar structure can enhance the solubility and dissociation ability of lithium salts to optimize ionic conductivity and improve rate performance, while their excellent thermal stability and the flame-retardant effect of decomposition products can also improve the battery thermal runaway threshold and enhance safety performance.

[0040] In some embodiments, sulfonyl compounds include at least one of 1,3-propenesulfonyl lactone and 1,3-propanesulfonyl lactone.

[0041] In some embodiments, the electrolyte further includes a lithium-containing compound, wherein the mass ratio of the lithium-containing compound to compound I is (0.5-1):(0.5-1).

[0042] In some embodiments, the lithium-containing compound includes at least one of lithium tetrafluoroborate and lithium difluorooxalate borate.

[0043] It is understandable that the mass ratio of the lithium-containing compound to compound I can be any value from 1:1, 1:2, 2:1, or any value within a range of any two values. Different lithium-containing compounds can provide additional protection for both the positive and negative electrodes. For example, boron-containing lithium salts preferentially oxidize at the positive electrode, forming a dense CEI film rich in BO bonds, effectively suppressing the dissolution of transition metals and the oxidative decomposition of the electrolyte under high voltage; while the DFOB anion in LiODFB... - It can generate a LiF-LiBOB composite SEI film at the negative electrode, enhancing mechanical strength and significantly reducing interfacial impedance, thus accelerating the Li... + Migration inhibits lithium dendrite growth.

[0044] In some embodiments, the electrolyte further includes an organic solvent and a lithium salt; The organic solvents include cyclic carbonates and chain carbonates; The lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, and lithium bistrifluoromethanesulfonylimide, and the lithium salt has a mass percentage of 12-15% in the electrolyte.

[0045] It is understandable that the mass percentage of lithium salt in the electrolyte can be any value from 12%, 13%, 14%, 15%, or any value within a range of two. By controlling the amount of lithium salt added to the electrolyte to meet the above range, it is possible to ensure that the electrolyte has good conductivity.

[0046] In some embodiments, cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, and chain carbonates include dimethyl carbonate and methyl ethyl carbonate; the total mass of the organic solvent is 100%, wherein the total mass percentage of fluoroethylene carbonate and ethylene carbonate is 20% to 23%, the mass percentage of dimethyl carbonate is 50% to 65%, and the mass percentage of methyl ethyl carbonate is 15% to 25%.

[0047] Understandably, cyclic carbonates have high dielectric constants and high viscosity, making them suitable for dissociating lithium salts, while chain carbonates have lower viscosity. When used as a co-solvent in combination with cyclic carbonates, they can improve the uniformity of the electrolyte. By controlling the organic solvents in the electrolyte to meet the above formulation, the overall viscosity and ionic conductivity of the electrolyte can be further optimized.

[0048] The third embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte of any one of claims 4 to 9; the high-temperature storage capacity retention rate (28 days, 60°C) of the lithium-ion battery is 88.9 to 92.4%, and the high-temperature cycle capacity retention rate (45°C, 350 cycles) is 86.2 to 89.8%.

[0049] Specifically, the above-mentioned lithium-ion battery can be prepared in the following manner: Graphite was used as the negative electrode active material. A negative electrode slurry was prepared by mixing graphite, conductive agent and binder in a mass percentage of 97.4:1.5:1.1. The negative electrode slurry was coated on a copper foil current collector and dried under vacuum to obtain a negative electrode sheet. Using NCM811 as the positive electrode active material, the positive electrode active material, conductive agent, and binder were prepared into a positive electrode slurry in a mass ratio of 96.5:1.7:1.8. The positive electrode slurry was coated onto an aluminum foil current collector and then vacuum dried to obtain the positive electrode sheet. A cylindrical battery is assembled using the electrolyte in any of the above embodiments, along with the positive electrode, negative electrode, and separator.

[0050] The electrolyte additive, electrolyte, and lithium-ion battery provided in this application are described below with reference to specific embodiments: Example 1 This embodiment provides an electrolyte additive composition and an electrolyte, as detailed below: Based on the mass percentage of the components, the electrolyte formulation used in this embodiment is as follows: Compound I-1: 0.5%, LiODFB: 0.5%, PS: 0.5%, LiPF6: 15%, with the balance being organic solvent components. The organic solvent components in the above electrolyte formulation consist of fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the organic solvent being 100%, the mass percentages are: fluoroethylene carbonate 3%, ethylene carbonate 20%, dimethyl carbonate 50%, and methyl ethyl carbonate 27%.

[0051] The electrolyte was prepared by the following method: under an argon atmosphere, compound I-1, lithium difluorooxalate borate, 1,3-propanesulfonate lactone, and lithium hexafluorophosphate were added to an organic solvent formed by mixing ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate, and the mixture was stirred and mixed at 10°C for 3 hours to obtain the electrolyte.

[0052] Example 2 This embodiment provides an electrolyte additive composition and an electrolyte, with the amount of electrolyte additive added as a variable, which is 0.7%, and the rest is the same as in Example 1.

[0053] Example 3 This embodiment provides an electrolyte additive composition and an electrolyte, with the amount of electrolyte additive added as a variable, which is 1%, and the rest is the same as in Example 1.

[0054] Example 4 This embodiment provides an electrolyte additive composition and an electrolyte, wherein the electrolyte additive is replaced with compound I-2, and the addition amount is 0.5%, and the rest is the same as in Example 1.

[0055] Example 5 This embodiment provides an electrolyte additive composition and an electrolyte, wherein the electrolyte additive is replaced with compound I-3, and the addition amount is 0.5%, and the rest is the same as in Example 1.

[0056] Example 6 This embodiment provides an electrolyte additive composition and an electrolyte, using the electrolyte formulation used in Example 1 as a reference, and the amount of sulfonyl lactone compounds included in the formulation as a variable. The difference from Example 1 is that the amount of PS added is adjusted to 0.7%, while the rest is the same as Example 1.

[0057] Example 7 This embodiment provides an electrolyte additive composition and an electrolyte, using the electrolyte formulation used in Example 1 as a reference, and the amount of sulfonyl lactone compounds included in the formulation as a variable. The difference from Example 1 is that the amount of PS added is adjusted to 1%, while the rest is the same as Example 1.

[0058] Example 8 This embodiment provides an electrolyte additive composition and an electrolyte, using the electrolyte formulation used in Example 1 as a reference, and the amount of sulfonyl lactones included in the formulation as a variable. The difference from Example 1 is that the amount of PS added is adjusted to 1%, and 1,3-propanesulfonyl lactone (PST) is added at an amount of 0.5%, while the rest is the same as in Example 1.

[0059] Example 9 This embodiment uses the electrolyte formulation used in Example 1 as a reference, and the types of lithium-containing compounds included in the formulation as variables. The difference from Example 1 is that the amount of LiODFB added is 1%, and everything else is the same as in Example 1.

[0060] Example 10 This embodiment uses the electrolyte formulation used in Example 1 as a reference, and the types of lithium-containing compounds included in the formulation as variables. The difference from Example 1 is that the amount of LiODFB added is 0.5%, and LiBF4 is added at an amount of 0.2%. Everything else is the same as in Example 1.

[0061] Example 11 This embodiment uses the electrolyte formulation used in Example 1 as a reference, with the content of lithium hexafluorophosphate in the formulation as a variable. The difference from Example 1 is that the content of lithium hexafluorophosphate is adjusted to 13.5%, and its content is reduced by the same mass as the organic solvent component used. Otherwise, it is the same as Example 1.

[0062] Example 12 This embodiment uses the electrolyte formulation used in Example 1 as a reference, with the content of lithium hexafluorophosphate in the formulation as a variable. The difference from Example 1 is that the content of lithium hexafluorophosphate is adjusted to 12%, and the content of the organic solvent component is reduced by the same mass. Otherwise, it is the same as Example 1.

[0063] Comparative Example 1 This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain electrolyte functional additives. Instead, the electrolyte functional additives in the electrolyte formulation of Example 1 are replaced by an equal amount of organic solvent components. Otherwise, it is the same as Example 1.

[0064] Battery performance test: 45℃ Cyclic Test: The above lithium-ion battery was placed at a high temperature of 45℃ for 3 hours, then charged at 1C constant current and constant voltage to 4.25V, and discharged at 1C constant current to 2.75V. This charge / discharge cycle was repeated 300 times, and the capacity retention rate of the lithium-ion battery was measured.

[0065] The capacity retention rate (%) of a lithium-ion battery after N cycles = discharge capacity of the Nth cycle / initial discharge capacity × 100%.

[0066] 60℃ Storage Test: The above lithium-ion battery was charged at 1C constant current and constant voltage to 4.25V at room temperature, and then discharged at 1C constant current to 2.75V, with an initial discharge capacity of C0. After that, the lithium-ion battery was charged at 1C constant current and constant voltage to 4.25V at room temperature, and then placed in a 60℃ constant temperature chamber for storage for 28 days. The reversible capacity of the battery was taken out every 7 days and recorded as Cn, where n is the number of days the lithium-ion battery was stored at high temperature.

[0067] The storage life of a lithium-ion battery after n days is = (Cn - C0) / C0 × 100%.

[0068] Test results as follows Figure 1 As shown in Table 1.

[0069] Table 1

[0070] As shown in Table 1, the electrolytes prepared in Examples 1-12 all contain the electrolyte additives provided in this application. When the electrolytes prepared in Examples 1-12 are applied to lithium-ion batteries, they all show significantly improved high-temperature storage performance and high-temperature cycling performance compared with Comparative Example 1. Based on the synergistic effect of the functional groups of the electrolyte functional additives, the electrolyte additives contain both vinyl sulfate groups and phosphoryl fluoride groups. The vinyl sulfate groups form a sulfur-containing SEI film on the negative electrode side to improve the diffusion efficiency of lithium ions. On the positive electrode, the phosphoryl fluoride derivative generates a P- and N-rich CEI film. The two groups work together to reduce the interfacial impedance of CEI / SEI, avoid the loss of active lithium, and improve high-temperature performance.

[0071] from Figure 1 As can be seen, the DCR growth rate decreases after the addition of functional additives, and the DCR growth rate gradually decreases as the amount of functional additives increases.

[0072] The electrolyte additives, electrolytes, and lithium-ion batteries provided in the embodiments of this application have been described in detail above. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrolyte additive characterized in that, Including compound I, the structural formula of which is shown in Formula I: Formula I; Wherein, R is selected from any one of halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted alkoxy; the substituent is selected from at least one of halogen, hydrocarbon and sulfate ester groups.

2. The electrolyte additive according to claim 1, characterized in that, The R is selected from any one of halogen, substituted or unsubstituted C2-C4 alkyl, C3-C5 alkenyl, C4-C6 alkynyl and substituted or unsubstituted C2-C4 alkoxy; the substituent is selected from at least one of halogen, C1-C3 hydrocarbon and vinyl sulfate group.

3. The electrolyte additive according to claim 1, characterized in that, Compound I is selected from any one of the compounds shown in Formulas I-1 to I-6: 。 4. An electrolyte, characterized by The electrolyte additive includes any one of claims 1 to 3, wherein the electrolyte additive is present in the electrolyte at a mass percentage of 0.5 to 1%.

5. The electrolyte according to claim 4, characterized in that It also includes sulfonyl lactones, wherein the mass ratio of the sulfonyl lactones to compound I is (0.5-1.5):(0.5-1).

6. The electrolyte according to claim 5, characterized in that The sulfonyl compounds include at least one of 1,3-propenesulfonyl lactone and 1,3-propanesulfonyl lactone.

7. The electrolyte according to claim 4, characterized in that, It also includes lithium-containing compounds, wherein the mass ratio of the lithium-containing compound to compound I is (0.5-1):(0.5-1).

8. The electrolyte according to claim 7, characterized in that, The lithium-containing compound includes at least one of lithium tetrafluoroborate and lithium difluorooxalate borate.

9. The electrolyte according to claim 4, characterized in that, It also includes organic solvents and lithium salts; The organic solvent includes cyclic carbonates and chain carbonates; The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium bis(trifluoromethylsulfonyl)imide, and the lithium salt has a mass percentage of 12-15% in the electrolyte.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is any one of claims 4 to 9; the high-temperature storage capacity retention rate (28 days, 60°C) of the lithium-ion battery is 88.9 to 92.4%, and the high-temperature cycling capacity retention rate (45°C, 350 cycles) is 86.2 to 89.8%.

Images